The present invention relates to an electrophotographic copier, printer, facsimile apparatus or similar image forming apparatus and more particularly to a finisher for finishing papers driven out of an image forming apparatus.
A finisher for the above application is taught in, e.g., Japanese Patent Laid-Open Publication No. 8-26579. The finisher includes a single tray mounted on one side thereof. A staple mode and a shift mode are available with the finisher. In the staple mode, papers sequentially driven out of an image forming apparatus are stacked on a staple tray disposed in the finisher, stapled together, and then discharged to the tray. In the shift mode, papers are directly discharged to the above tray without being stapled. The tray may be constructed to be movable up and down in order to stack a great number of papers, as also proposed in the past.
The above finisher has a paper outlet where a drive roller and a driven roller are arranged in a pair. The driven roller is rotatably mounted on one end of a roller support member that is angularly movable about the other end. The driven roller is pressed against the drive roller due to its own weight. In the shift mode, the drive roller and driven roller are held in contact with each other for discharging the papers. In the staple mode, the roller support member is angularly moved to release the driven roller from the drive roller.
However, the problem with this type of finisher is that all the groups of papers or all the stacks of papers are loaded on the single tray and cannot be distinguished from each other. This is particularly true when a plurality of persons share the finisher. Moreover, an image forming apparatus with such a finisher is often used as a printer for a computer or an output device for a facsimile apparatus. As a result, copies and printings are apt to exist together on the tray. This makes the distinction between copies produced by different persons and between copies and printings extremely difficult.
In light of the above, the finisher may be provided with another paper outlet and another tray or proof tray in addition to the above tray. Even this kind of scheme has a problem that because the outlets and trays are provided in one-to-one correspondence, various functions including a sort mode and a staple mode available with the finisher are limited. Specifically, when the proof tray is selected, stapling or similar advanced function is not available.
Japanese Patent Laid-Open Publication Nos. 9-48557 and 9-48559, for example, each disclose a finisher including a plurality of trays arranged one above the other and capable of locating one of them at a paper outlet. This kind of finisher, however, has the following problems left unsolved. The trays selected and the trays not selected each are moved across the outlet while only the tray selected is located at the outlet. Therefore, to prevent papers stacked on any one of trays from returning into the outlet, a shutter or similar sophisticated device must be arranged in the outlet.
Moreover, the trays each have an end fence for positioning the trailing edges of papers stacked thereon. Because the end fence is implemented by the wall of the finisher where the outlet is formed, an outlet roller cannot overlap the wall. As a result, although the trailing edge of a paper may successfully move away from the outlet roller, the paper is apt to partly remain between the outlet roller and the wall of the finisher. The finisher therefore fails to surely discharge papers.
Japanese Patent Laid-Open Publication No. 9-110259, for example, proposes a finisher addressing the above problems. The finisher taught in this document includes an outlet roller disposed in a paper outlet formed in the wall of the finisher. The outlet roller is movable toward and away from the paper outlet. After the trailing edge of a paper has reached the above wall, the outlet roller is moved away from the wall so as to prevent the trailing edge of the paper from remaining between it and the wall. This, however, complicates the arrangement of the paper outlet.
The finisher of Laid-Open Publication No. 9-48559 mentioned earlier has another problem left unsolved. After a tray unit has been moved to locate a designated tray at the single paper outlet, papers are discharged to the tray. As a result, the operation for discharging the papers must be delayed by a period of time necessary for the particular tray to reach the paper outlet.
Japanese Patent Laid-Open Publication No. 7-228401, for example, proposes a finisher constructed to reduce the above period of time and adaptive to a high-speed image forming apparatus. This finisher includes two paper outlets and two trays associated one-to-one with the paper outlets. The trays are arranged one above the other and movable up and down independently of each other. When the upper tray is used as a mass paper tray, the lower tray is retracted downward as soon as the upper tray is lowered to a preselected position. However, the paper outlets each being associated with a particular tray are sophisticated.
Japanese Patent Laid-Open Publication No. 8-73107 teaches a sorter capable of moving a plurality of trays up and down at the same time and varying the distance between nearby trays. The sorter allows the number of papers to be stacked on each tray to be varied, as desired. Each tray is movable via a paper outlet and is returned to its home position when papers are removed therefrom. However, the problem with this sorter is that all the trays are connected together and limit the stroke available for mass paper discharge, i.e., a sufficient capacity is not available for mass paper discharge.
In the finisher of the type locating one of a plurality of trays at a paper outlet by driving it independently of the other trays, when an upper tray should be brought to the paper outlet, a lower tray must be retracted downward away from the paper outlet. Also, when the lower tray should be brought to the paper outlet, the upper tray must be retracted upward away from the paper outlet. When the lower tray is used as a mass paper tray, it should preferably be retracted away from the paper outlet as far as possible from the capacity standpoint. This, however, increases a distance that the lower tray should be brought to the paper outlet when selected later, slowing down the finishing operation.
Further, Japanese Patent Laid-Open Publication No. 8-119518 discloses a finisher including a plurality of trays arranged one above the other and at least one of which is movable up and down for mass paper discharge. When the movable tray is selected, it is moved from a stand-by position where papers have been removed to a paper outlet. That is, the finisher taught in the above document recognizes a position where papers have been removed as a stand-by position. In practice, however, the movable tray sometimes reaches its lower limit position in the event of mass paper discharge. It follows that a substantial period of time is necessary for the tray to move from the stand-by position (lower limit position) to the paper outlet. The lower limit position of the mass paper discharge tray is naturally close to the bottom of the finisher, so that the function of the tray can be made most of. This increases the period of time necessary for the tray to move from the lower limit position to the paper outlet and is therefore apt to lower the processing speed of the image forming apparatus. To solve this problem, the moving speed of the tray must be varied by sophisticated control, as needed.
When a paper jams the paper outlet in any one of the conventional finishers, the operator must put the operator's hand in the paper outlet and move outlet rollers provided in a pair away from each other, i.e., rotate a roller support member for removing the paper. At this instant, the tray moving upward via the paper outlet is apt to injure the operator and damage structural elements around the paper outlet. Although the shutter taught in Laid-Open Publication No. 9-48557 or 9-48559 may obviate such an accident, it sophisticates the configuration of the outlet and control.